Multistage refrigerating system



w; E. DODSON 2,386,198

MULTISTAGE REFRIGERATING SYSTEM Oct. 9; 1945.

' Filed Feb. 8. 1944 Inventor Wagne E. Dodson,

b5 mM/M His Attorngg.

Patented Oct. 9, 1945 MULTISTAGE REFRIGERATING SYSTEM Wayne E. Dodson,Caldwell, N. .I., assignor to General Electric Company, a corporation ofNew York Application February 8, 1944, Serial No. 521,520

2 Claims. (Cl. 62-115) My invention relates to multi-stage compressionrefrigerating systems for producing very low temperatures.

Refrigerating systems provided with multistage compressors may beemployed to obtain very low temperatures and for cooling test rooms andthe like The compressed refrigerant flowing from a low stage compressorto a higher stage compressor may contain superheat and it is desirableto remove this superheat before admitting the gas to the higher stagecompressor. It is also desirable that the liquid refrigerant supplied tothe evaporator have as much heat as possible removed from it before itflows through the pressure reducing device or expansion valve. Theamount of cooling required for removing the superheat from thecompressed gas in the interstage connection and the amount of coolingrequired for subcooling the liquid refrigerant on its way to theexpansion valve vary over considerable ranges and it is desirable thatsome arrangement be provided for controlling the cooling of the liquidand of the interstage gas. It is an object of my invention to provide amulti-stage compression refrigerating system including an improvedarrangement for controlling the subcooling of the liquid refrigerant onits way to the evaporator and for controlling the removal of superheatfrom the gas in the connection between two compression stages.

Further objects and advantages of my invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of my invention reference may be had to theaccompanying drawing the single figure of which illustratesdiagrammatically a two-stage compression refrigerating system embodyingmy invention.

Briefly, the refrigerating system illustrated in the drawing comprises arefrigerating system having two compressors or two compressor cylindersarranged to operate at different pressures and connected in series in a,refrigerant circuit including a condenser, a liquid receiver, and anevaporator controlled by a thermostatic expansion valve. The refrigerantcircuit between the receiver and the expansion valve includes a liquidsubcooler and two bleed-off connections, one for supplying refrigerantto cool the subcooler and the other for supplying refrigerant to theconnections between the two compressor cylinders.

The two bleeder circuits are separately controlled system shown in thesingle figure thereof includes an evaporator Ill arranged to cool theair within a thermally insulated compartment II. The evaporator isconnected in the circuit of a refrigerating system including a lowpressure compressor i2 and a high'pressure compressor l3, a condenser I4and a liquid receiver ii. The compressors l2 and I3 may be separatelydriven or may comprise low and high stage cylinders of a singlecompressor, these alternative constructions- .being well known in theart. The condenser I4 is provided with a, surrounding casing it throughwhich cooling water may be circulated to absorb heat from the hotcompressed refrigerant in the condenser; this absorption of heatcondenses and liquefies the refrigerant which flows into the liquidreceiver 15. The liquid refrigerant collects in the receiver l5 andflows therefrom through a liquid line including a coil II arranged in acasing IS, the casing l8 being connected in the suction line of thecompressor cylinder l2 between the cylinder and the evaporator in sothat the cold gas returned to the compressor absorbs heat from theliquid refrigerant in the coil i1 and cools it. Heat exchangers of thistype are commonly employed to improve the efficiency of refrigeratingsystems. After flowing through the main heat exchanger, Just described,the liquid refrigerant flows through a U-shaped coil or conduit sectionl9 and then through a pressure regulating valve 20. The valve 20 reducesthe pressure of the refrigerant to a predetermined value before it flowsto the main expansion valve illustrated as a thermostatic expansionvalve 2|. The expansion valve is provided. with a temperature responsiveelement or feeler bulb 22 arranged in heat exchange relation with thesuction line at the outlet of the evaporator iii. In order to subcoolthe liquid refrigerant passing through the coil [9 a jacket 28 isarranged about the coil and liquid refrigerant from the liquid line isbled to the jacket 23' through a connection 24 under control of athercasing 23 is vaporized at the interstage pressure, and the vaporizedrefrigerant is withdrawn by operation of the high pressure compressorIS, the casing 23 being connected in communication with the interstageconnection between the compressors l2 and it which is indicated at 27.The valve 25 then operates to provide adequate subcooling of the liquidin the coil l9.

In order to control the temperature of the refrigerant admitted to thesecond stage compressor l3 and thereby to de-superheat the gas flowingfrom the compressor I! to the compressor It, a bypass or bleederconnection 28 is provided between the liquid line and the interstageconnection 21 and is controlled by a temperature responsive valve 30having a thermal feeler bulb 3| responsive to the temperature of therefrigerant admitted to the intake of the compressor I3. A

temperature control valve for controlling the temperature of therefrigerant flowing to a higher pressure compressor of a multi-stagecompression refrigerating system is disclosed and broadly claimed in acopending application of Harold F. Lathrop, Serial No. 521,518, filedFeb. 8, 1944, and assigned to the same asslgnee as the presentinvention.

By providing independent control of the subcooler and a separate bleederfor obtaining refrigerant to cool the gas in the interstage connectionunder control of the temperature responsive valve, the refrigeratingsystem is made to operate over a wide range of conditions, for example,adequate subcooling is provided at all times whether or not refrigerantis required for cooling the interstage gas. Furthermore, adequateinterstage cooling may be provided whether or not subcooling isrequired. The subcooler and the interstage cooler functioning togetherin the arrangement illustrated provide a very efficient refrigeratingsystem which is effective to produce ver low temperatures under a widerange of operating conditions.

While I have described my invention in connection with a two-stage watercooled refrigerating system, other applications will readily be apparentto those skilled in the art. I do not, therefore, desire my invention tobe limited to particular arrangements shown and described and I intendby the appended claims to cover all modifications within the spirit andscope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A multi-stage refrigerating system comprising highand low pressurecompressors, an evaporator and a condenser, an interstage connection forconveying refrigerant from the outlet of said low pressure compressor tothe inlet of said high pressure compressor, a liquid line for conductingliquid refrigerant from said condenser to said evaporator, a heatexchanger for subcooling the liquid in a portion of said line, meansproviding two parallel paths for bleeding refrigerant from said liquidline to said interstage connection, one of said paths being arranged tosupply refrigerant to said heat exchanger and the other of said pathscommunicating directly with said interstage connection, means forcontrolling the flow of refrigerant through said first path inaccordance with a condition of said subcooler, and means responsive tothe temperature of the refrigerant at the inlet of said high pressurecompressor for controlling the flow of refrigerant through said secondpath.

2. A multi-stage refrigerating system comprising high and low pressurecompressors, an evaporator and a condenser, an interstage connection forconveying refrigerant from the outlet of said low pressure compressor tothe inlet of said high pressure compressor, a liquid line for conductingliquefied refrigerant from said condenser to said evaporator, a heatexchanger for subcooling the liquid in a portion of said line, means forbleeding refrigerant from said line to supply said heat exchanger andfor conducting refrigerant vaporized in said heatexchanger to saidinterstage connection, means for bleeding refrigerant from said linedirectly to said interstage connection, a thermostatic expansion valvefor controlling the flow of refrigerant to cool said heat exchanger, andmeans responsive to the temperature of the refrigerant at the inlet ofsaid high pressure compressor for controlling the flow of refrigerantthrough said second bleeding means.

WAYNE E. DODSON.

